CO2 - the major cause of global warming

Global warming is caused by the emission of greenhouse gases . 72% of the totally emitted greenhouse gases is carbon dioxide (CO2), 18% Methane and 9% Nitrous oxide (NOx). Carbon dioxide emissions therefore are the most important cause of global warming. CO2 is inevitably created by burning fuels like e.g. oil, natural gas, diesel, organic-diesel, petrol, organic-petrol, ethanol. The emissions of CO2 have been dramatically increased within the last 50 years and are still increasing by almost 3% each year, see graph below:

Graph 1: CO2-emissions world-wide by year (data from wri.org)

Graph 2: CO2 emissions world-wide by year and CO2 concentration in the atmosphere by year

The carbon dioxide is released to the atmosphere where it remains for 100 to 200 years. This leads to an increasing concentration of carbon dioxide in our atmosphere (see above on the right hand side), which in turn causes the average temperature on Earth to raise (see graph below).

Chart 3: Increase of global average temperature for the last 20 years (source: wri.org)

Recent investigations have shown that inconceivable catastrophic changes in the environment will take place if the global temperatures increase by more than 2° C (3.6° F). A warming of 2° C (3.6° F) corresponds to a carbon dioxide (CO2) concentration of about 450 ppm (parts per million) in the atmosphere.

As of beginning of 2007, the CO2 concentration is already at 380 ppm and it raises on average 2 - 3 ppm each year, so that the critical value will be reached in approximately 20 to 30 years from now. See here for some graphs about the increasing concentration of greenhouse gases and the greenhouse gas emissions by sector.

Mitigation goals for the main cause of global warming: carbon dioxide emissions

As a result of the above mentioned findings, there seems to be a consensus among the leading developed countries that the temperature increase caused by global warming must not exceed 2° C (3.6° F). For example the European Union (EU) has committed itself to this threshold already in 2005.

To reach this target the annual global CO2 emissions have to be reduced from about 28 Gigatons in 2006 to 20 Gigatons of CO2 by the year 2050 and to 10 Gigatons of CO2 by the year 2100 according to IPCC. At the first glance, this does not look like a major reduction. However one should keep in mind that the world population will grow from 6.4 billion people in 2007 to about 9.5 billion people in 2050. At the same time more and more developing countries will progress their industrialisation and as a result they will want to copy our western life style causing high CO2 emissions.

The world-wide average CO2 emissions by capita was about 4 tons per year in 2005. For North America it was about 20 tons and for Europe about 10 tons per year per capita. By 2050, the world-wide average CO2 emission per capita needs to be reduced to 2 tons per year. In the following years, the emissions will need again to be cut by half. Download and use our Excel calculator to simulate cause and effects of global warming . Based on an average carbon footprint, you can test ways to mitigate global warming yourself. Alternatively, you can have a look at some simulation results how global warming can be stopped below 2 C.

In a fair world, there is absolutely no justification for the western world to pollute the Earth more than others. So we should aim to reduce our carbon footprint to 2 tons per capita per year until 2050. This means people in industrialised nations will have to cut down their carbon dioxide emissions to values reaching 10% to 20% of the current values.

Water vapor is indeed the most important naturally occurring greenhouse gas. The major natural greenhouse gases are water vapor, which causes about 36-70% of the greenhouse effect on Earth (not including clouds); carbon dioxide CO2, which causes 9-26%; methane, which causes 4-9%, and ozone, which causes 3-7%. It is not possible to state that a certain gas causes a certain percentage of the greenhouse effect, because the influences of the various gases are not additive. Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons.

But the fact that water vapor is the most important gas in creating the natural greenhouse effect does not mean man-made greenhouse gases have no effect!

Since we cannot influence the naturally occurring greenhouse gases, we normally concentrate on the man-made greenhouse gases (many times without specifically mentioning). Sometimes they are called "emitted greenhouse gases". I understand that this can be confusing.

Increasing amounts of man-made greenhouse gases lead to an increase in the surface temperature on Earth. This temperature increase causes other effects, one of them being the increase of the amount of water vapor in the atmosphere. Although human activities do not directly add significant amounts of water vapor to the atmosphere, warmer air can contain more water vapor. Because water vapor is a greenhouse gas (as you mentioned), global warming will be further enhanced by the increased amounts of water vapor. This is called a positive feedback.

In other words:

The current global warming is caused by man-made greenhouse gases (mainly CO2, NOx and Methane).

Global warming leads to a higher temperature on Earth.

Due to the higher temperature, the air does contain more water vapor.

This additional water vapor (a greenhouse gas) does again increase the effect of global warming (a positive feedback or secondary effect).

The Earth has indeed already had warming periods for several times, as you mentioned. However there is not just one single way to initiate a global warming period. Who is saying that all global warming periods have been caused by the same effect?

So earlier warming periods may easily have been caused by different effects than the current one. In fact, most of the earlier global warming periods have been caused by a change in the sun's radiation. In that particular case it is normal that the CO2 concentration lags behind the warming because it is a secondary effect and not the cause.

The current global warming however is caused by man-made emissions of greenhouse gases. It is meanwhile well proven not to be a natural cycle.

You can fracture your leg with skiing, but you can also fracture your leg if you fall down the stairs. If you fractured your leg already two times with skiing, this is no proof that in the third case it was caused by skiing as well. Maybe you have had a car accident or anything else.

It is similar with the cause of global warming: The cause for earlier warming periods can be (and indeed are) different from the current one.

Compared to the water vapor which is already in the atmosphere, the additional water vapor generated by hydrogen-powered cars would have very little influence.

The problem with hydrogen-powered cars is the generation of hydrogen. At the time being, there is no very efficient and clean technology available for the creation of such amounts of hydrogen.

We can turn it as we want: we will have to reduce our energy requirements in the developed world. We are definitely consuming too many resources. Our current lifestyle is very far away from being a sustainable one.

You need to look at the yearly average temperature. Just to take one month and then draw conclusions is not appropriate. All in all, the wheather is getting more extreme, so we will have much wormer and much colder days, weeks and months in a year. We will have periodes with extremely high precipitations and periodes with aridity. The same is true for storms, tornados, etc.

What you see in the graph above is the yearly average temperature of the world (not just in the place where you are living). And this yearly average temperature of the world has been increasing.

For example, let's look at burning diesel fuel. Burning fuel is called an oxidation process. To make it simple, we assume C12H26 as chemical formula for diesel fuel. Then the following chemical reaction takes place:

2 C12H22 + 37 O2 → 26 H2O + 24 CO2

This means: for each kg of diesel fuel burnt, 1.38 kg water vapor and 3.106 kg CO2 is produced. So the oxidation of diesel fuel creates more than two times as much carbon dioxide (CO2) as water vapor. The relation for other fossil fuels is similar (but not exactly the same).

I am certainly not denying the effect of water for the (natural) greenhouse effect. However, if you took 12'000 molecules of air, you would normally find just 3 molecules of CO2 but 600 molecules of water. So if you add 26 more water molecules to 600, the relative change is quite little compared to adding 24 carbon dioxide molecules to the existing 3 CO2 molecules.

However, it is not just the number of molecules as you seem to suggest: the strength of greenhouse effect of the different contributors also needs to be taken into account. With increasing height, the concentration of water vapor drops significantly, where the concentration of other greenhouse gases like CO2 or Methane remain more or less constant with increasing height above ground. Because it is colder up there, greenhouse gases are much more effective with increasing height above ground.

Water vapor and clouds account for about 65 to 85% of the natural greenhouse effect (natural means without human acitivities). The remaining 15 to 35% of the natural greenhouse effect are caused by very small concentrations of the other greenhouse gases (CO2, NOx, Methane, etc.). This explains why relatively small quantities of CO2 and other non-water greenhouse gases can have a major effect on the climate.

Human beings have been increasing the amount of non-water vapor greenhouse gases in the atmosphere (mainly due to burning fossile fuels, cattle breeding, etc.). This causes the temperature to rise. In addition, an increased temperature causes more water to water to evaporate into the atmosphere, which does in turn increase the warming effect.

The air is a mixture of different compounds, usually about 21% oxygen (O2) and about 78% nitrogen (N2). We have this mixture although nitrogen is lighter than oxygen. So the same question can be asked for nitrogen and oxygen in the air.

The anwser is: Air is a so-called meta-stable gas mixture, the concentrations remain constant up to a height of about 100 kilometers. The air is constantly agitated (e.g. by winds) which helps to keep it
well mixed and to lower existing differences in concentration.

Emission of CO:

A modern vehicle should not emit much CO because CO is a sign of a bad (incomplete) burning process. Usually because oxygen was missing. The catalyst in the vehicle should convert CO into CO2.

CO is dangerous for human beings and for plants. Just mixing it with oxygen is not enough to transform it into CO2, it needs further activation (catalyst, sun light, etc.)